The Face on the Milk Carton by Caroline B. Cooney

Janie Johnson is eating lunch one day when she notices the picture on the milk carton of a missing child. The missing child is a picture of her when she was little. She remembers the dress and gradually remembers other things about her past. She loves her parents, but are they really her parents? Where is her birth certificate? Why aren't their any pictures of her when she was little? Should she try to contact her real parents, who she doesn't even remember or stay with the parents she knows and loves?